Re: BUG: Bad page map in process udevd (anon_vma: (null)) in 2.6.38-rc4

[David Miller <davem@davemloft.net>]

From: Linus Torvalds <torvalds@linux-foundation.org>
Date: Thu, 17 Feb 2011 20:30:42 -0800

> On Thu, Feb 17, 2011 at 7:16 PM, Eric W. Biederman
> <ebiederm@xmission.com> wrote:
>> BUG: unable to handle kernel paging request at ffff8801adf8d760
>> IP: [<ffffffff8140c7ca>] unregister_netdevice_queue+0x3a/0xb0
> 
> Yup. That's the "list_move()". The disassembly is exactly what I'd
> expect from __list_del():
> 
>   16:	48 8b 93 a0 00 00 00 	mov    0xa0(%rbx),%rdx
>   1d:	48 8b 83 a8 00 00 00 	mov    0xa8(%rbx),%rax
>   24:	48 8d bb a0 00 00 00 	lea    0xa0(%rbx),%rdi
>   2b:*	48 89 42 08          	mov    %rax,0x8(%rdx)     <-- trapping instruction
>   2f:	48 89 10             	mov    %rdx,(%rax)
> 
> So I think we can consider this confirmed: it really is the stale
> queue left over on the stack (introduced by commit 443457242beb). With
> CONFIG_DEBUG_PAGEALLOC, you get a page fault when it tries to update
> the now stale pointers.
> 
> The patch from Eric Dumazet (which adds a few more cases to my patch
> and hopefully catches them all) almost certainly fixes this rather
> nasty memory corruption.

Eric D., please get a final version of the fix posted to netdev and
I'll make sure it slithers it's way to Linus's tree :-)

Thanks!

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